The modern aircraft instrument panels have a display system comprising several display devices. One or more display devices display the information necessary to the piloting or navigation. The information displayed originates from the sensors of the aircraft, from a geolocation system of the “GPS” (Global Positioning System) type and from the inertial system of the aircraft. The measurement system as a whole supplies at least the following parameters: position of the aircraft in latitude, longitude and altitude and orientation of the aircraft in pitch, roll and heading. These display screens are known as “Primary Flight Display”, with the acronym “PFD”.
Generally, these screens also comprise a synthetic representation of the outside landscape. This representation is derived from a system called “SVS”, the acronym for “Synthetic Vision System”. An SVS system comprises a mapping database representative of the terrain flown over, a geolocation system and graphic computation means. The image displayed is a three-dimensional view of the outside represented as realistically as possible. The viewpoint displayed is in the axis of the aircraft. These screens can also display, instead of the SVS, a real image of the outside landscape, derived from a system called “EVS”, the acronym for “Enhanced Vision System”, or display this real image superimposed on the synthetic view of the outside landscape, which is then called “CVS”, the acronym for “Combined Vision System”.
When a PFD screen comprises a synthetic image of the landscape, a large quantity of information is represented and it is essential, when an abnormal situation occurs, for the pilot to be aware of it as quickly as possible. That happens notably when the carrier is in an unusual attitude, for example when the roll or the pitch of the aircraft are too high. The unusual attitude situation may occur for various reasons such as, for example, the loss of outside visual references in bad weather or the inattention of the pilot subject to an excessive workload or searching for a reference on the ground. This unusual attitude position can, in addition, be aggravated if there is a deviation between the visual and sensory perceptions of the pilot and the instrument indications. This deviation may originate from a failure on the instrument indications or from a bad interpretation of the physical sensations of the pilot.
To assist the pilot in coming out of an unusual attitude, the display on the PFD is of great importance. It must allow the pilot to easily find his or her bearings, notably the orientation of the aeroplane relative to the sky and to the earth. This is all the more obvious when the synthetic image displays only the terrain, a situation called “brown-over-brown”, or only the sky, a situation called “blue-over-blue”, or even a portion of sky and a portion of sea, both represented in blue, even if the blues are substantially different.
To assist the pilot in knowing where the sky and the earth are located in unusual attitudes, it is common practice to have a permanent display of two circular arcs 10 and 11, a blue arc on the sky side and a brown arc on the earth side, as shown in FIG. 1 which schematically represents a PFD screen. For clarity, in this figure, the image of the terrain is symbolized by a simple crest line 12 and the symbology is highly simplified. This representation has a number of drawbacks. In nominal mode, these circular arcs are useless and therefore overload the display. In degraded mode corresponding to the unusual attitudes, they are not sufficiently visible and therefore do not provide the necessary assistance to the pilot.
To overcome these drawbacks, other solutions have been proposed. Thus, the U.S. Pat. No. 7,724,155 entitled “Graphical methods for enhancing attitude awareness” proposes various graphic solutions making it possible to indicate the sky/earth separation. In a first configuration, the sky/earth information is at the periphery of the display area and is not therefore in the primary area where the gaze of the pilot is focused. It may then be that the pilot does not pay sufficient attention to this information. Furthermore, in case of unusual attitude, only a small portion corresponding to the sky or to the earth is visible, because the separation of the two portions is determined by the position of the line representing the zero longitudinal trim indicator, also called “ZPRL”, the acronym for “Zero Pitch Reference Line”. The pilot needs more time to assimilate the information and comprehend the orientation of the aeroplane. In a second configuration, the sky/earth information is on either side of the ZPRL. It is well inside the primary area where the gaze of the pilot is focused but the information strip is thin, so the two items of information are very close together, and it is then possible for the pilot not to sufficiently well distinguish between what is above and what is below the ZPRL. Furthermore, in conditions where the position of the ZPRL is at the edge of the screen, the sky/earth information is no longer in the primary area where the gaze of the pilot is focused. Here again, it is possible for the pilot not to pay sufficient attention to this information.
The application US 2010/0141482 entitled “System and method for rendering a primary flight display” proposes solutions similar to those described above and has the same drawbacks.
The U.S. Pat. No. 8,767,013 entitled “System and method for rendering a sky veil on a vehicle display” describes a display where the sky is presented in semi-transparency to avoid the so-called “brown-over-brown” situations. However, when the position of the ZPRL is at the edge of the screen, only a small portion corresponding to the sky or to the earth is visible, and the pilot needs longer to assimilate the information and comprehend the orientation of the aeroplane. Furthermore, the colour of the transparent sky is identical to the colour of the synthetic sky, making it impossible to distinguish the transparent sky from the synthetic sky and therefore making the information more unclear.